Free space optical conditioner

Abstract

An optical communications terminal, comprising: an optical telescope (e.g. a dual mirror Ritchie-Chretien telescope); a transmitter unit including at least one transmitter coupled to source of optical signals; a receiver unit for receiving optical signals; an optical system defining a transmit optical path between the optical telescope and the transmitter unit, and defining a receive optical path between the optical telescope and the receiver unit; and a beacon detector for detecting beacon optical signals received at the optical telescope; characterised in that a beacon optical path between the optical telescope and the beacon detector comprises at least a portion of said transmit optical path and/or said receive optical path. In one embodiment, the transmitter unit, receiver unit and beacon detector are disposed at or adjacent the focal plane of the optical telescope, providing a compact arrangement suitable for usage in diverse environments (e.g. aircraft- or satellite-borne, as well as ground-based). In another aspect of the invention there is disclosed an optical communications terminal in which the transmitter unit comprises a plurality of transmitters, each transmitter being coupled to a respective source of optical signals. An optical free space communications system comprising two such coupled terminals is also disclosed.

1 . An optical communications terminal, comprising: 
 an optical telescope;    a transmitter unit including at least one transmitter coupled to source of optical signals;    a receiver unit for receiving optical signals;    an optical system defining a transmit optical path between the optical telescope and the transmitter unit, and defining a receive optical path between the optical telescope and the receiver unit; and a beacon detector for detecting beacon optical signals received at the optical telescope;    characterised in that a beacon optical path between the optical telescope and the beacon detector comprises at least a portion of said transmit optical path and/or said receive optical path.    
   
   
       2 . The terminal of  claim 1 , wherein the transmitter unit, receiver unit and beacon detector are disposed at or adjacent the focal plane of the optical telescope.  
   
   
       3 . The terminal of  claim 1 , wherein the optical system includes a relay lens and a first mirror, and the optical path between said first mirror and the optical telescope is common to the transmit optical path, the receive optical path and the beacon optical path.  
   
   
       4 . The terminal of  claim 3 , wherein the optical system includes a beamsplitter between the first mirror and the receiver unit, the beamsplitter, in use, passing receiver optical signals along the transmit optical path to the receiver unit and reflecting beacon optical signals along the beacon optical path to the beacon.  
   
   
       5 . The terminal of  claim 1 , wherein the transmitter unit includes a plurality of transmitters.  
   
   
       6 . The terminal of  claim 1 , wherein for at least one of said at least one transmitter an aperture is provided in the first mirror, a separate transmit optical path thereby being provided from at least one of said at least one transmitter to the optical telescope via a respective aperture.  
   
   
       7 . The terminal of  claim 1 , wherein said at least one transmitter comprises the terminating portion of a single mode optical fibre, a collimating lens preferably being provided at said terminating portion in a respective transmit optical path.  
   
   
       8 . The terminal of  claim 5 , wherein each transmitter is fed by the same optical signal.  
   
   
       9 . The terminal of  claim 5 , wherein each transmitter is fed by a different optical signal.  
   
   
       10 . The terminal of  claim 5 , wherein there are three transmitters.  
   
   
       11 . The terminal of  claim 4 , wherein the beacon optical path includes a second focussing lens between said beamsplitter and the beacon detector.  
   
   
       12 . The terminal of  claim 11 , wherein the beacon optical path includes a filter system between said second focussing lens and the beam detector, the filter system preferably including, in sequence, a filter passing a first predetermined frequency and a neutral density filter.  
   
   
       13 . The terminal of  claim 11 , wherein the first predetermined frequency is 830 nm.  
   
   
       14 . The terminal of  claim 1 , wherein, the receiver unit includes one receiver for receiving optical signals at a second predetermined frequency, different to said first predetermined frequency, said second predetermined frequency preferably being 1550 nm.  
   
   
       15 . The terminal of  claim 14 , wherein the receiver comprises a terminating portion of a multimode optical fibre.  
   
   
       16 . An optical communications terminal, comprising: 
 an optical telescope;    a transmitter unit coupled to source of optical signals;    a receiver unit for receiving optical signals;    an optical system defining a transmit optical path between the optical telescope and the transmitter unit, and defining a receive optical path between the optical telescope and the transmitter unit; and    characterised in that the transmitter unit comprises a plurality of transmitters, each transmitter being coupled to a respective source of optical signals.    
   
   
       17 . The terminal of  claim 16 , wherein for at least one of said plurality of transmitters an aperture is provided in the first mirror, a separate transmit optical path thereby being provided from said at least one of said plurality of transmitters to the optical telescope via a respective aperture.  
   
   
       18 . The terminal of  claim 16 , wherein at least one of said plurality of transmitters comprises the terminating portion of a single mode optical fibre, a collimating lens preferably being provided at said terminating portion in a respective transmit optical path.  
   
   
       19 . The terminal of  claim 16 , wherein each transmitter is fed by the same optical signal.  
   
   
       20 . The terminal of  claim 16 , wherein each transmitter is fed by a different optical signal.  
   
   
       21 . The terminal of  claim 16 , wherein there are three transmitters.  
   
   
       22 . The terminal of  claim 16 , further including a beacon detector for detecting beacon optical signals received at the optical telescope.  
   
   
       23 . The terminal of  claim 22 , wherein the transmitter unit, receiver unit and beacon detector are disposed at or adjacent the focal plane of the optical telescope.  
   
   
       24 . The terminal of  claim 22 , wherein the optical system includes a relay lens and a first mirror, and the optical path between said first mirror and the optical telescope is common to the transmit optical path, the receive optical path and the beacon optical path.  
   
   
       25 . The terminal of  claim 24 , wherein the optical system includes a beamsplitter between the first mirror and the receiver unit, the beamsplitter, in use, passing receiver optical signals along the transmit optical path to the receiver unit and reflecting beacon optical signals along the beacon optical path to the beacon.  
   
   
       26 . The terminal of  claim 22 , wherein the beacon optical path includes a second focussing lens between said beamsplitter and the beacon detector.  
   
   
       27 . The terminal of  claim 22 , wherein the beacon optical path includes a filter system between said second focussing lens and the beam detector, the filter system preferably including, in sequence, a filter passing a first predetermined frequency and a neutral density filter.  
   
   
       28 . The terminal of  claim 22 , wherein the first predetermined frequency is 830 nm.  
   
   
       29 . The terminal of  claim 22 , wherein the receiver unit includes one receiver for receiving optical signals at a second predetermined frequency, different to said first predetermined frequency, said second predetermined frequency preferably being 1550 nm.  
   
   
       30 . The terminal of  claim 29 , wherein the receiver comprises a terminating portion of a multimode optical fibre.  
   
   
       31 . An optical free space communications system, comprising: 
 a first optical communications terminal, the first optical communications terminal being a terminal according to any of the preceding claims; and    a second optical communications terminal, the second optical communications terminal being a terminal according to  claim 1;     wherein the first optical communications terminal and the second optical communications terminal are arranged whereby, in use, the transmitter unit of the first optical communications terminal may transmit said optical signals to the receiver unit of the second optical communications terminal and the transmitter unit of the second optical communications terminal may transmit said optical signals to the receiver unit of the first optical communications terminal.    
   
   
       32 . A method of making an optical communications terminal, comprising: 
 providing an optical telescope;    providing a transmitter unit including at least one transmitter coupled to source of optical signals;    providing a receiver unit for receiving optical signals;    providing an optical system defining a transmit optical path between the optical telescope and the transmitter unit, and defining a receive optical path between the optical telescope and the receiver unit;    providing a beacon detector for detecting beacon optical signals received at the optical telescope; and    characterised in that a beacon optical path between the optical telescope and the beacon detector comprises at least a portion of said transmit optical path and/or said receive optical path.    
   
   
       33 . A method of using an optical communications terminal, said optical communications terminal comprising: 
 an optical telescope;    a transmitter unit including at least one transmitter coupled to source of optical signals;    a receiver unit for receiving optical signals;    an optical system defining a transmit optical path between the optical telescope and the transmitter unit, and defining a receive optical path between the optical telescope and the receiver unit; and    a beacon detector for detecting beacon optical signals received at the optical telescope;    characterised in that a beacon optical path between the optical telescope and the beacon detector comprises at least a portion of said transmit optical path and/or said receive optical path; and    said method comprising receiving optical signals in said receiver unit.    
   
   
       34 . A method of making an optical communications terminal, comprising: 
 providing an optical telescope;    providing a transmitter unit coupled to source of optical signals;    providing a receiver unit for receiving optical signals;    providing an optical system defining a transmit optical path between the optical telescope and the transmitter unit, and defining a receive optical path between the optical telescope and the transmitter unit; and    characterised in that the transmitter unit comprises a plurality of transmitters, each transmitter being coupled to a respective source of optical signals.    
   
   
       35 . A method of using an optical communications terminal, said optical communications terminal comprising: 
 an optical telescope;    a transmitter unit coupled to source of optical signals;    a receiver unit for receiving optical signals;    an optical system defining a transmit optical path between the optical telescope and the transmitter unit, and defining a receive optical path between the optical telescope and the transmitter unit;    characterised in that the transmitter unit comprises a plurality of transmitters, each transmitter being coupled to a respective source of optical signals; and    said method comprising receiving optical signals in said receiver unit.